Fix `AzureComponentFactory` is null (#274)

src/SignalRServiceExtension/Config/SignalRWebJobsBuilderExtensions.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
+using Microsoft.Extensions.Azure;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.Azure.WebJobs.Extensions.SignalRService
@@ -25,6 +26,7 @@ namespace Microsoft.Azure.WebJobs.Extensions.SignalRService
             }
 
             builder.AddExtension<SignalRConfigProvider>();
+            builder.Services.AddAzureClientsCore();
             builder.Services.AddSingleton<IServiceManagerStore, ServiceManagerStore>();
             return builder;
         }